Thanks for getting in touch!
We are aware of this issue and it is a regression in Xamarin Studios. They already have a fix for this issue which will they'll be releasing in their next service release.
The issue is caused in Xamarin.iOS version 10.4.0.123.
We recommend users roll back their Xamarin.iOS version to the previous working version (10.3.1.8) until Xamarin release their fix.
For more information, see our conversation with Xamarin regarding this issue here.
Let me know if you have any questions.